How do you use a referral code on roblox?

There are two different kinds of referrals on Roblox.

1. When you make an account (if 3 people use your referral for this you'll get the Inviter badge.)

2. When somebody gets Builder's Club (any kind.) If somebody uses your referral code, you and the other user will get 400 ROBUX each.

You can find your referral code here.

http://www.roblox.com/Upgrades/BuildersClub.aspx